Foreign ministers and international diplomats were meeting in Geneva with governments still in dispute over whether Syrian President Bashar al-Assad, condemned in the West but still backed by Russia, could have any role in a political transition.
"The Russians have set out a series of objections with the current draft. The Russians are stonewalling quite a bit," a Western diplomat told Reuters as the talks paused for lunch.
"A redraft of the text is looking likely," she said, referring to Annan's draft proposal.
Annan, the former UN chief and the special international envoy on Syria, is hoping for consensus on a plan for a unity government that would exclude controversial figures from leadership - effectively meaning Assad would step down.
"We are here to agree on guidelines and principles for a Syrian-led political transition that meets the legitimate aspirations of the Syrian people," he said in opening remarks.
"No one should be in any doubt as to the extreme dangers posed by the conflict - to Syrians, to the region, and to the world."
His appeal gave a note of urgency to the need for world powers to move closer in their positions as the 16-month-old conflict in Syria deepens. His plan for a negotiated solution is the only one on the table.
Moscow objects to any solution imposed on Syria from outside. The United States and its European and Arab allies see no way ahead while power remains in Assad's hands.
As the diplomats gathered at the UN complex by the shores of Lake Geneva, the Syrian army rained mortar fire on pro-opposition areas in Deir al-Zor, Homs, Idlib and the outskirts of Damascus, opposition activists said.
Government troops were fighting rebels of the Free Syria Army in several places. Syria's border with Turkey was also tense following a Turkish military build-up in response to Syria's shooting down of a Turkish warplane last week.
More than 10,000 people have been killed since the anti-Assad uprising broke out and the past few weeks have been among the bloodiest.
DIVIDE AND FAIL
Annan said the crisis should never have reached this point. "Either unite to secure your common interests or divide and surely fail in your own individual way. Without your unity, your common resolve and your action now ... nobody can win and everyone will lose in some way," he said.
The mood of pessimism was reinforced by a senior US official who said the talks might not reach a deal on Saturday.
"Discussions remain challenging," the official said. British foreign secretary William Hague said Assad and his close associates could not lead any transition. Accountability for war crimes must be part of such a process, he added in his speech to the meeting.
Hague called for the UN security council to start drafting a resolution next week setting out sanctions against Syria, a move that he noted put him at at odds with Russia.
The foreign ministers of the five permanent members of the UN Security Council - Russia, the United States, China, France and Britain - were all attending the talks along with Turkey, Kuwait, Qatar, UN secretary-general BanKi-moon League chief Nabil Elaraby and the EU's Ashton.
Also present was Norwegian Major General Robert Mood, who headed a failed UN ceasefire monitoring mission to Syria and was witness to some of the violence.
Iran, Syria's closest regional ally, and Saudi Arabia, a foe of both Damascus and Tehran and leading backer of the rebel forces opposing Assad, are not represented. Nor is anyone from the Syrian government or opposition.
According to a draft document from Annan, seen by Reuters, the envoy envisages the setting up a transitional government of national unity which can establish a neutral environment for political change. It would have full executive powers.
"It could include members of the present government and the opposition and other groups, but would exclude from government those whose continued presence and participation would undermine the credibility of the transition and jeopardize stability and reconciliation," it said.
That proposal is the stumbling block as it effectively means Assad cannot be involved, which Moscow and Beijing views as imposing a solution. The Syrian opposition also demands that he be barred from any role.
United nations chief Ban, opening the closed-door meeting, underlined the need to reach an agreement "today".
Edited By Cen Fox Post Team
